Conversion is an event when there is individual or collective change in religion or religious affiliation. It is part of a longer process in which the beliefs, habits, identities, and rituals of a new religion are adopted and adapted by a community. In the Middle Ages, conversion was often a collective experience and a top-down process. Some conversion was forced upon communities. More organic or bottom-up processes, triggered by trade or migration, are often harder to document but were certainly important.